This invention relates to scanning microscopes used for imaging the topography of surfaces and, more particularly, to an atomic force microscope having extended use capabilities comprising, a horizontal base member; a scan tube vertically supported at a bottom end by the base member and having a top surface for holding a sample to be scanned and moveable in x-, y-, and z-directions as a result of scanning voltages applied thereto; first support means extending upward from the base member; a sample holding block having a chamber therein, the sample holding block having a first bore communicating with the chamber through a bottom surface, a second bore communicating with the chamber through a top surface, and a third bore communicating with the chamber at an acute angle to the second bore, the sample holding block being positioned with the scan tube passing through the first bore and supported by the first support means; second support means extending upward from the bottom surface into the chamber, a probe-carrying module having a probe attached thereto and extending downward therefrom at an acute angle with a tip of the probe positioned to contact a sample mounted on the top surface of the scan tube, the probe carried by the probe-carrying module comprising a substrate attached to the probe-carrying module and a pair of arms of a smooth-surfaced, minimally self-biased material cantilevered outward from a bottom front edge of the substrate in a V-shape to form an optical lever, the pair of arms having a probe point at the apex of the V-shape thereof; a source of a laser beam mounted for directing the laser beam down the second bore from the top surface of the sample holding block to strike the probe and be reflected down the third bore to an outer end thereof; and, photoelectric sensor means having an active surface positioned over the outer end of the third bore for developing an electrical signal at an output thereof reflecting the position on the active surface at which the laser beam strikes the active surface.
The family of scanning probe microscopes that have been introduced to the scientific community of recent years is broadening the frontiers of microscopy. As typified by the greatly simplified general example of FIGS. 1 and 2, these microscopes scan a sharp probe 10 over the surface 12 of a sample 14 to obtain surface contours, in some cases actually down to the atomic scale. The probe 10 may be affixed to a scanning mechanism and moved in a scan pattern over the surface 12 or alternately (and equally effectively because of the small sizes involved) the probe 10 may be stationary with the sample 14 mounted on a scanning mechanism that moves the surface 12 across the probe 10 in a scanning pattern. The tip 16 of the probe 10 rides over the surface 12 as the probe 10 is moved across it. As the tip 16 follows the topography of the surface 12, the probe 10 moves up and down as indicated by the bi-directional arrow 18. This up and down movement of the probe 10 is sensed to develop a signal which is indicative of the z directional component of the 3-dimensional surface 12.
Early atomic force microscopes (AFMs) mounted the probe 10 to a wire and electrically sensed the movement of the wire as the probe tip 16 moved over the surface 12. Recent prior art AFMs employ technology developed in the microelectronics art as depicted in FIG. 1. It should be noted that the drawings figures herein are not to scale as the probe 10 and its tip 16 (typically of a diamond material) are extremely small so as to be useful at the near-atomic level. If the drawings were drawn to scale, these components would not be visible. In fact, when working with AFMs, these components are not visible to the naked eye and must be viewed with an optical microscope. As will be seen shortly, this is a source of some of the problems which are solved by this invention.
As depicted in FIG. 1, recent prior art AFMs have the probe 10 extending outward from the forward edge of a substrate 20 with the probe 10 being formed thereat by manufacturing techniques which are not critical to the present invention. It is sufficient to point out that the probe 10 is typically in the form of an arm extending outward from the substrate 20 with the diamond tip 16 attached at the end of the arm. Also, the probe 10 is extremely small and extremely fragile. The substrate 20 is typically adhesively attached to the bottom and extending outward from the forward edge of a large steel block 22 mounted to the surrounding structure. Where the probe 10 and sample 14 are conductive, the position of the probe 10 as a result of the deflection caused by the surface 12 during the scanning process can be sensed electrically. Where non-conductive samples are to be scanned, the prior art literature suggests bouncing a laser beam 24 off the probe 10 to be sensed by a photoelectric sensor 26. As depicted in FIG. 2, as the probe 10 deflects up and down, the reflection angle of the laser beam 24 is changed. It is this change in reflection angle that is sensed by the photoelectric sensor 26, which then outputs an electrical signal related to the angle (by way of the beam of light striking a detecting surface), and thereby the z directional component of the probe 10.
Regardless of the probe positional sensing method employing (electrical or laser light), there are a number of problems associated with the prior art AFMs as typified by the simplified drawings of FIGS. 1 and 2. As depicted in FIG. 2, the surface 12 of a sample 14 has a thin (i.e. molecular level) coating of water 28 thereon. Often, the small, lightweight tip 16 of the probe 10 is "sucked" into the surface 12 against the miniscule resilient biasing force of the probe 10 by the capillary action of this coating of water 28. This, of course, can seriously damage the tip 16 to the point of making it non-useful for its intended purpose. Further on the negative side, the coating of water 28 is not sufficient to provide any lubricating with respect to the tip 16 sliding over the surface 12. As a result, frictional wear of the tip 16 is a serious problem causing the tip 16 to wear off quickly to the point of making it non-useful of its intended purpose. Also, with some sample materials the tip 16 may dig into and damage the sample surface 12 rather than sliding over it to provide useful information. Additionally, the scanning action is accomplished by the application of fairly high voltages to a scanning member. With the steel mounting block 22 in close proximity as depicted in FIG. 1, these voltages can be attracted to the steel block 22 and, in the process, affect the probe 10 thereby introducing false data into the output stream.
The type of environment and class of persons who are and will be using AFMs in the future also adds to the problems of this extremely useful and potentially powerful device. Typically, the user is a researcher working on various projects in a laboratory environment. He/she is not interested in having to "play" with the AFM to get it to produce workable results. In its present configuration as depicted by the drawings of FIGS. 1 and 2, it is difficult of set up for scanning. It is easy to break the tip 16 from the probe 10 and/or the probe 10 from the substrate 20. Replacing the probe/tip assembly is a major undertaking; and, because of the problems described above, the life expectancy of the probe/tip is extremely short. Moreover, the sample 14 is glued to the top of a piezoelectric scanning tube (not shown in FIGS. 1 or 2) which provides the scanning action by moving the sample with respect to the stationary probe 10 (which must remain fixed in position to have the laser beam 24 reflect from it for detection purposes). Thus, once placed, the sample 14 is impossible to move (so as to change the scanning point) and difficult to change. Positioning the tip 16 of the probe 10 on the surface 12 of the sample 14 is difficult at best and virtually impossible in some cases. In short, while AFMs are moving into a commercial stage of development, the products which are available in the prior art are not the efficient, easy to use laboratory aids that the users thereof desire and need.
Wherefore, it is an object of the present invention to provide an AFM system which is easy to set up, calibrate, and use in the typical laboratory environment by the typical laboratory worker.
It is another object of the present invention to provide an AFM system in which the probe/tip resist frictional wear.
It is still another object of the present invention to provide an AFM system in which the probe/tip are not subjected to the capillary forces of water coating the surface of the sample.
It is yet another object of the present inventio to provide an AFM system in which the probe/tip slide easily over the sample surface and resist digging into softer samples and damaging them thereby providing a gentler and more reliable operation.
It is a further object of the present invention to provide an AFM system in which the probe/tip are contained in an easily replaceable module which is recyclable by the AFM supplier.
It is a still further object of the present invention to provide an AFM system having calibration/setup tools included therewith which make the setting up of the AFM a simple and straightforward task.
It is another object of the present invention to provide an AFM system in which the sample is held by a removeable and adjustable member which allows the position of the sample to be changed in situ and allows a new sample to be installed easily and quickly without destruction of previous samples.
It is also an object of the present invention to provide an AFM system in which the steel mounting block of the prior art is removed without affecting the stability of the probe and tip.
Other objects and benefits of this invention will become apparent from the description which follows hereinafter when taken in conjunction with the drawing figures which accompany it.